A former Brooklyn police sergeant, fired after stealing $40 from a drug dealer to pay an informant, yesterday was spared a jail sentence — but told, instead, to become a role model for kids.

Michael Arenella, 32, who had faced up to 25 years in prison on corruption charges, was sentenced to just 160 hours of community service.

Saying he believed Arenella, had intended to use the dealer’s cash in 2007 to get information that could take drugs off the streets, Brooklyn Supreme Court Judge Gustin Reichbach ordered him to serve as a mentor to teens in the Big Brothers program.